Upgrade cloud_print from deprecated base::JSONReader API

Bug: 1070409
Change-Id: I577dfb61d70ac8048f08fa13502753ee62b24e86
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2228592Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Nigel Tao <nigeltao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#775050}

chrome/browser/printing/cloud_print/privet_url_loader.cc

@@ -250,8 +250,8 @@ void PrivetURLLoader::OnDownloadedToString(
     return;
   }
 
-  base::JSONReader json_reader(base::JSON_ALLOW_TRAILING_COMMAS);
-  base::Optional<base::Value> value = json_reader.ReadToValue(*response_body);
+  base::Optional<base::Value> value =
+      base::JSONReader::Read(*response_body, base::JSON_ALLOW_TRAILING_COMMAS);
   if (!value || !value->is_dict()) {
     delegate_->OnError(0, JSON_PARSE_ERROR);
     return;